Patent GB-1093370-A (GB)
Title: Polyolefine ropes and other cordage
Inventor: WARD IAN MACMILLAN
IPC: D01F6/04
Filed: 1966-01-17
Abstract: Ropes and other cordage comprise ribbons, filaments or fibres composed of a stereo-regular propylene/olefin copolymer have at least 60% by weight of propylene therein, said ribbons, filaments or fibres having an extensional modulus of at least 65 g.p.d. and a torsional recovery not exceeding 55%.  Preferably, the comonomer with propylene in the copolymer is ethylene, but in general any monoolefin readily copolymerisable with propylene, may be used. Ribbons and filaments for use in the invention may be produced by melt-extrusion of the molten polymer which is extruded through a spinneret or die and subjected to longitudinal tension which causes the material to elongate while it is still in the plastic state, cooling and solidification eventually terminating this process of elongation referred to as 'draw-down'.  Filaments so made are then subjected to second stage drawing, either as part of the extrusion process or more usually as a separate process supplying extruded yarn to the drawing process from a temporary package.  Drawing may be effected by simply tensioning the yarn sufficiently or preferably by passing the yarn over a heated snubbing surface or through a heating chamber, the amount of heat supplied to the yarn and the time of heating of the drawing process being insufficient to convert it to the plastic state.  In order that ribbons or filaments having extensional or torsional properties suitable for use in the invention are produced it is necessary to apply a high-draw ratio to the material in the longitudinal drawing step, a value approaching close to the maximum operable draw ratio being preferred.  In the case of a copolymer having more than 80% by weight of propylene therein a draw ratio of at least 12:1 is preferred.  Ribbon filaments for use in the invention may also be produced from melt-extruded longitudinally drawn films by slitting the film before or after drawing to narrow strips.  Likewise ribbons or filaments may be cut into staple lengths for processing into ropes according to the invention on machinery designed for operation with staple fibres.  Conventional rope making methods are used.  Ropes according to the invention have unusual or desirable properties as for example low creep (residual extension on repeated tensional loading) and high flexibility, which renders such ropes easier to use in certain circumstances, than ropes made from natural fibres. In an example a propylene/ethylene copolymer containing 15% by weight of ethylene and melt-flow index (A.S.T.M. D1238-57) 12 is melt spun at 275 DEG C through a spinneret having a single 0.052 inch diameter orifice into a water bath at 85 DEG C and wound up at 50 ft. per min.  The spun filament is longitudinally drawn at a draw ratio of 12.5:1 using a tubular, electrically heated, radiant heater at an air temperature of 250 DEG C, (measured at a point inside the heater close to the filament) as the heating means. The drawn filament has a denier of 744, and extensional modulus of 90 g.p.d., a torsional recovery of 40% and a tenacity of 6.2 g.p.d. A 1 3/4 inch circumference 3-strand laid rope constructed from these filaments has a breaking load of 2.28 tons and a creep (residual extension after 120 repeat loadings to 75% of the breaking load, expressed as a percentage of the original length) of 10%.